Salt Stress and Tomato Resilience: From Somatic to Intergenerational Priming Memory

To ameliorate plants’ response to environmental stresses, seed priming can be a useful tool; it consists of the pre-exposure of the seeds to mild stress, which improves plant adaptation to future exposure to adverse growth conditions. In our previous studies, seed priming with polyamines (2.5 mM putrescine, 2.5 mM spermine, and 2.5 mM spermidine) and salt acclimation have been proven to be an effective treatment in enhancing salt tolerance of tomato cultivars since they induced a better physiological response to salt stressful condition. The persistence of the memory of the first (priming) stress and retrieval of such remembered information upon exposure to later new stress play an important role in the applicability of seed priming in agriculture. Therefore, the aim of this work was the detection of the persistence of a stress memory induced by polyamine priming in tomatoes. Primed and not-primed seeds were stored at +4 °C for 2 years after the original priming treatment; then, germinated seeds were sown in non-saline soil and irrigated with 80 and 160 mM NaCl salt solutions until fruit production. The results confirm the increase in salt tolerance in primed plants compared to not-primed ones, indicating the presence of long-term somatic memory. In comparison with not primed, the primed plants produced better quality fruits, i.e., higher weight, water content, and higher amount of carotenoids, soluble sugars, and phenols. To determine if the memory can be inherited by the offspring, seeds were then collected from primed and not-primed plants (generation G1), and further experiments were undertaken by growing G1 plants under the same irrigation regime as the parental generation. After 45 days of growth, both antioxidants and osmolyte amounts were enhanced, leading to an improvement in the tolerance to saline conditions in the offspring of primed plants and confirming the results already observed in the parental generation. These results demonstrate, for the first time, the presence of both long-term somatic and intergenerational priming memory in tomatoes and may pave the pathway to future agricultural application of seed priming.